Abstract

New aeromagnetic data resolve the dykes of the Falkland Islands into three swarms. A hitherto unrecognized suite of north–south dykes is established as early Cretaceous by an Ar–Ar date of about 121 Ma. Swarms of NE–SW and east–west dykes are both early Jurassic: the former gives an Ar–Ar age of about 178 Ma, whereas the latter has been previously dated to about 190 Ma. The intrusion of the Cretaceous dykes marks the onset of oceanic crust generation in the South Atlantic and so restricts to mid-Jurassic the microplate rotation envisaged in most models for the Falklands break-out from Gondwana.